Retractor device with oximeter sensor and force sensor

ABSTRACT

A retractor device has an oximeter sensor at its tip, which allows measuring of oxygen saturation of a tissue being retracted by the retractor. The retractor device also has a force sensor which can measure an amount of force that is applied to the retracted tissue by the tip of the retractor device. The tip includes one or more openings for at least one source and detector. A specific implementation is a spinal nerve root retractor with an oximeter sensor and a force sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/689,053, filed Jan. 18, 2010, issued as U.S. Pat. No.8,688,186 on Apr. 1, 2014, which claims the benefit of U.S. provisionalpatent application 61/149,916, filed Feb. 4, 2009, which areincorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to the field of medical devices and morespecifically to a retractor device with an oximeter sensor and forcesensor.

Retractors play an important role in medicine. Retractors typicallyretract or hold aside tissue so that a physician (e.g., surgeon) cangain access to an area for operation or observation. It is important tonot damage the tissue when retracting the tissue.

One area of medicine that retractors are commonly used is during spinalsurgery. Tens of thousands of spinal surgeries are performed each year.The number of spinal surgeries is continuing to increase due, in part,to an aging population, active lifestyles, and a better understanding ofwhat causes back pain. Back pain may be due to disc herniation,degenerative disc disease, spinal trauma, and osteoarthritis just toname a few examples.

The spinal cord is the main pathway through which the brain sends andreceives signals. The nerve fibers in the spinal cord branch off to formpairs of nerve roots that travel through small openings between thevertebrae. These nerves control the body's function including the vitalorgans, sensation, and movement.

During spinal surgery, it is often necessary to retract, or hold, thenerve root aside so that the surgeon can access the surgical site. Withcurrent medical devices, however, it is difficult if not impossible, totell whether the nerve root is being damaged during the retraction.Damage to the nerve root or any nerve is undesirable—leading to loss ofsensation, numbness, or pain to patient.

There is, then, a continuing demand for medical devices that providepatient feedback, provide more features, are easier to use, andgenerally address the needs of patients, doctors, and others in themedical community.

Therefore, there is a need to provide improved devices and techniquesfor retractors.

BRIEF SUMMARY OF THE INVENTION

A retractor device has a retractor including a shaft, a handle connectedto a proximal end of the shaft, and a tip connected to a distal end ofthe shaft, where the tip has a retractor portion and an oximeter sensor.The retractor device further includes a force sensor that is operativelyconnected to the retractor.

The oximeter sensor in the device measures oxygen saturation of a tissuebeing retracted by the retractor device. The force sensor measures anamount of force applied to a retracted tissue by the tip of theretractor device. Thus, the retractor device can simultaneously measuretwo parameters of a retracted tissue—oxygen saturation level of theretracted tissue contacting the tip of the retractor device and anamount of force applied to the retracted tissue by the tip.

In one implementation, the retractor device is a nerve root retractordevice for retracting a nerve. The tissue oxygen saturation sensingcapability can potentially prevent nerve root hypoxia during spinalsurgical retraction. In addition, force sensor measurements allow asurgeon to monitor and adjust an amount of force applied to a retractedtissue during surgery. Thus, the use of an excessive amount of force,which can potentially damage a tissue, can be avoided during retraction.By having both oximeter sensor and force sensor, the retractor devicecan better assist determining the effect of surgical manipulation on thehealth of nerve roots and other tissues.

In another implementation, the retractor device has a force sensor thatis an integral part of a retractor, and the force sensor can be locatedat any suitable location between a handle and a tip of the retractor.For instance, the force sensor has a first end and a second end, thefirst end and the second end being on opposite side of each other alongthe axis of the force sensor. The first end of the force sensor can beattached to the handle of the retractor, and the second end of the forcesensor can be attached to a proximal end of a shaft of the retractor.

In yet another embodiment, the retractor device can have a force sensoras a separate attachment to the retractor. For instance, the first endof the force sensor is attached to the handle of the retractor by aclamp. The second end of the force sensor is attached to a separatehandgrip element or second handle. A surgeon can hold the handgripelement or second handle (not the handle on the retractor itself) toretract a tissue, and an amount of force that is applied to the tissueby the tip of the retractor device is measured by the force sensor.

In yet another implementation, the retractor device has an oximetersensor including a first sensor opening and a second sensor opening on abottom side of the tip. There is a first optical fiber and a secondoptical fiber. The first optical fiber passes through a channel in theshaft and a distal end of the first optical fiber is connected to thefirst sensor opening of the tip. The second optical fiber passes throughthe channel in the shaft and a distal end of the second optical fiber isconnected to the second sensor opening of the tip.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a retractor device with an oximetersensor and a load cell, and other components.

FIG. 2 shows details of an embodiment of a retractor device.

FIG. 3 shows a photograph of mechanical parts of a retractor device.

FIG. 4A shows a calibration setup of a load cell, with the axis of theload cell being vertical.

FIG. 4B shows a calibration setup of a retractor device having a loadcell, with the axis of the load cell being vertical.

FIG. 5 shows a calibration setup of a retractor device having a loadcell, with the axis of the load cell being horizontal.

FIG. 6A shows a side view of a retractor device and a direction of forceapplied.

FIG. 6B shows a top view of the retractor device shown in FIG. 6A.

FIG. 7 shows a perspective view of a first implementation of a tip.

FIG. 8 shows a bottom view of the first implementation of a tip.

FIG. 9 shows a perspective view of a second implementation of a tip.

FIG. 10 shows a bottom view of the second implementation of a tip.

FIG. 11 shows a perspective view of a third implementation of a tip.

FIG. 12 shows a bottom view of the third implementation of a tip.

FIG. 13 shows a side view of the third implementation of a tip.

FIG. 14 shows a perspective view of the third implementation of the tipattached to a nerve retractor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram of a retractor device 100 that is used forretracting a tissue, such as a nerve root. Retractor device 100 can alsobe used to measure oxygen saturation of the retracted tissue and anamount of force applied to the tissue during retraction. FIG. 1 alsoshows an oximeter console 133 and a load cell interface 129 which areconnected to components of retractor device 100.

Retractor device 100 has an oximeter retractor tip 103 which isconnected to a force sensor or load cell 106, which is in turn connectedto a handle 109. Oximeter retractor tip 103 includes a retractor portionwhich is used to retract a tissue and an oximeter sensor which is usedto measure oxygen saturation level of the tissue contacting the tip. Theretractor device is used by placing the oximeter sensor at the retractortip in contact with a tissue such as a nerve, and the tissue is pulledaside by the retractor tip.

Load cell 106 in the retractor device measures an amount of force thatis applied to the tissue by oximeter retractor tip 103 when a surgeonholds handle 109 and retracts or pulls aside the tissue. Load cell 106is a transducer that converts a force or load acting on it into anelectrical signal. When there are changes in the force or load, therewill be a change in the electrical signal produced by the load cell. Theload cell can be located at any suitable location between oximeterretractor tip 103 and handle 109.

Oximeter console 133 is connected to an oximeter sensor located atoximeter retractor tip 103 by a cable. Light is transmitted fromoximeter console 133, through optical fiber in the cable, out a sensoropening on the tip and into the nerve. The reflected light from thenerve is then received by another sensor opening at the tip, transmittedback to the oximeter console via optical fiber. The oximeter consoleprocesses and analyzes light information or signals using algorithms andconverts the signals into oxygen saturation values in terms ofpercentage. The oximeter console can include a screen to display theoxygen saturation measurement and the timing of measurement. Themeasurements can also be stored in the oximeter console.

Load cell interface 129 is connected to load cell 106 of the retractordevice by a cable. The signal from load cell 106 is transmitted to loadcell interface 129 directly or via circuitry. The load cell interfacetransforms the electrical signals from the load cell into a force orother measurement or reading, which can be shown on a display.

While oximeter console 133 and load cell console 129 are shown asseparate blocks in FIG. 1, these components can be enclosed in a singlehousing (e.g., a console or computer), or in separate housings. Forexample, the load cell interface may be incorporated within oximeterconsole 133. Alternatively, some subcomponents of oximeter console 133and load cell interface 129 can be combined into a single housing whileother subcomponents are housed separately.

FIG. 2 shows one embodiment of a retractor device. A retractor device210 includes a retractor that has a first handle 213, a shaft 216connected at its proximal end 219 to the first handle, and a tip 222connected to a distal end 225 of the shaft. The shaft can be made ofsteel. The tip includes a retractor portion or retractor blade 228 andan oximeter sensor 231. Oximeter sensor 231 has one or more sensoropenings 230 on a bottom surface of the oximeter sensor, adjacent toretractor blade 228.

The shaft can include an internal channel or passageway. Optical fiberscan pass from sensor openings on the tip, through the channel, throughthe handle, and into a cable jacket or cable insulation. Alternatively,the fibers can be run along the shaft and secured by, for example,shrink wrap. The optical fibers that travel inside or along the shaftare exposed through sensor opening 230 on a bottom surface of tip 222.Cable 276 that includes optical fibers is configured to be connected toa system unit or oximeter console (not shown).

Retractor device 210 also includes a force sensor 255. Force sensor 255has a first end 257 and a second end 259 on the opposite side of thefirst end along the axis of force sensor 255. Force sensor 255 measuresan amount of force that is applied in a horizontal direction along itsaxis. First end 257 of force sensor 255 is connected to an L-shapedclamp element 243. L-shaped clamp element 243, together with linearclamp element 241, is clamped to first handle 213 of the retractor by afastener 215. Second end 259 of force sensor 255 is connected to asecond handle 265. Force sensor 255 also has a cable 275 which transmitsa signal measured by force sensor 255 to a system unit or force sensorconsole (not shown).

Retractor device 210 can be used by placing oximeter sensor 231 incontact with a nerve. Light is transmitted from a system unit or console(not shown in FIG. 2), through optical fiber in cable 276, out a sensoropening 230 on tip 222 and into the nerve. The reflected light from thenerve is then received by another sensor opening on the tip, transmittedback to the console via optical fiber, and then processed. The consolecan display oxygen saturation measurement. The same or separate consolecan also display an amount of force that is applied by the retractor tipto retract the nerve.

Retractor device 210 has two handles—first handle 213 and second handle265. When first handle 213 is used to retract a tissue, there is nochange in load or force for load cell 255 as it is not being pulledupon. When the tissue is retracted using first handle 213, oxygensaturation measurements of a retracted tissue can be made. However, aforce applied to a retracted tissue will not be measured.

When second handle 265 is used to retract a tissue, since the handle isconnected to load cell 255, a strain gauge in load cell 255 becomesdeformed as the surgeon pulls second handle 265 to retract a tissue. Theload or force measured by load cell 255 is converted into an electricalsignal which is transmitted to a system unit (not shown) via cable 275.When the tissue is retracted using second handle 265, both oxygensaturation and force measurements can be made.

While FIG. 2 illustrates an embodiment of the invention where the forcesensor is attached to a retractor as a separate unit and is pulled uponby a second handle, the force sensor can be an integral part of theretractor itself. For example, the force sensor can be located betweenfirst handle 213 and proximal end 219 of the shaft of the retractor. Inanother example, the force sensor can be located in the middle of shaft216. In yet another example, the force sensor can be located betweendistal end 225 of the shaft and retractor tip 222. When the force sensoris integrated as part of a retractor, second handle 265 can be omittedin the device, and first handle 213 can be used to retract or pull asidea tissue.

FIG. 3 shows a photograph of mechanics of a retractor device 300.Retractor device 300 has a retractor 310 that has a tip with an oximetersensor at a distal end. A handle of retractor 310 is attached to one endof a load cell 355 by a clamp 342. The opposite side of load cell 355 isattached to an aluminum handle 365. The load cell can sense a loadranging between zero to ten pounds. A cable 315 connects load cell 355to a system unit (not shown). A cable 313 connects the oximeter sensorat the tip of retractor 310 to a system unit (not shown).

FIGS. 4A, 4B, and 5 illustrate various setups for calibrating a loadcell. Shown in FIGS. 4A, 4B, and 5 is a load cell, such as from CooperInstruments & Systems, Model LPM 530-HW10 (Warrenton, Va.). The datasheet and users' guide for this load cell is incorporated by referencealong with all other references cited in this application. According tothe factory calibration, the load cell and amplifier provide one volt ofoutput per one pound of force. The factory calibration is verified byusing the setups shown in FIGS. 4A, 4B, and 5.

In FIG. 4A, a poise is attached to one end of the axis of the load cell,and a handle is attached to the other end of the axis of the load cell.As shown in FIG. 4A, the axis of the load cell is vertical. A cable fromthe load cell is connected to an amplifier, which is then connected to avoltmeter. Therefore, an LCD reading on the voltmeter represents theweight of the poise that is hung vertically on the load cell.

In a first calibration, no poise was attached to the load cell. In asecond calibration, a poise weighing 200 grams was attached. In a thirdcalibration, a poise weighing 400 grams was attached. The results areshown in table A.

In the first calibration for the setup shown in FIG. 4A, the voltmeterreading was 0.04 volt. Since no poise was attached in this setup, 0.04volt represents an offset that is subtracted from the voltmeter readingwhen weights are attached to the load cell. Accordingly, the calibrationequation for the setup shown in FIG. 4A is as follows:[force used on the load cell]=([LCD reading]−0.04 volt)*4.9 Newton.

This equation agrees with the factory calibration with an error of about5 percent. It is noted that one kilogram of force equals 2.205 pound offorce, which equals 9.8 Newton.

In FIG. 4B, a retractor device shown in FIG. 3 was used to calibrate apoise. As shown in FIG. 4B, the retractor device is held by a secondhandle attached to a load cell so that the axis of the load cell isvertical. A poise is hung at the tip of the retractor device. Again,voltage measurements were made with zero weight, with a poise weighing200 grams, and with a poise weighing 400 grams. The results are shown intable A.

When no weight was attached for the setup shown in FIG. 4B, thevoltmeter reading was 0.22 volt. Since no poise is attached in thissetup, 0.22 volt represents a force due to the weight of the retractordevice. Therefore, if the retractor device is to be used as shown inFIG. 4B (i.e., with a force on the retractor device tip being vertical),then the calibration equation is as follows:[Vertical force used on the retractor tip]=([LCD reading]−0.22 Volt)*4.9Newton.

FIG. 5 shows how a retractor device is used in retracting a tissue. Inthis figure, the second handle pulls on a load cell horizontally to theleft to retract a tissue. The voltmeter reading without hanging anypoise is 0.1 volt as shown in the last column of table A. Therefore, thecalibration equation for the setup shown in FIG. 5 is as follows:[horizontal force on the retractor tip]=([LCD reading]−0.1 volt)*4.9Newton.

For example, when a retracting force of two Newton is executed onto theretractor device tip along the horizontal direction in FIG. 5, thevoltmeter reading should be about 0.51 volt.

TABLE A Calibration Results Weight LCD reading (Volt) (gram) Figure 4AFigure 4B Figure 5 0 0.04 0.22 0.1 200 0.47 0.62 400 0.97 1.04

FIG. 6A illustrates a side view of a retractor device. As shown in FIG.6A, the retractor device has a force sensor 615 that is connectedbetween an oximeter retractor 610 and a handle 618. Force sensor 615measures an amount of force applied to a tissue 630 by a retractor tip622 when handle 618 is pulled to the right to retract the tissue. Aretractor portion 612 cradles tissue 630 so that the tissue is ready tobe pulled, and oximeter sensor 613 measures an oxygen saturation levelof tissue 630 at the point of contact.

Typically, oximeter retractor 610 has a shaft that is angled to assist asurgeon in viewing or retracting a tissue. For example, the shaft may bebent at an angle 627 of about 105 degrees as shown in FIG. 6A. Angle 627shown in FIG. 6A is merely exemplary, and the shaft may be bent at anysuitable angle ranging between 90 and 179 degrees. However, in anembodiment, the shaft can be straight with angle 627 of 180 degrees, andthe retractor device is a straight puller.

FIG. 6B illustrates a top view of the same retractor device shown inFIG. 6A. As shown, the retractor device includes force sensor 615 whichis connected between a tip of oximeter retractor 610 and handle 618,ready to pull nerve 630 resting near tip 622 of the retractor device.

In FIGS. 6A and 6B, when the retractor device is pulled by handle 618 ina horizontal direction to the right, nerve 630 is pulled away from itsoriginal, resting position to the right. The distance that nerve 630travels at the point of contact is referred to as a “retractiondistance,” shown as d_(r) in FIG. 6A. When handle 618 pulls theretractor device to the right, then a retraction distance of nerve 630increases. When the retractor device is returned back to the left, thena retraction distance decreases to a point where the retraction distanceequals zero as shown in FIGS. 6A and 6B.

FIG. 7 shows a perspective view of a first implementation of a tip 705.The tip includes a retractor blade and an oximeter sensor 710 attachedto a top surface 715 of the tip. The tip attaches to a shaft 720. Thetip also includes a retractor portion 723. Optical fibers are encased ina cable jacket 725, travel along the shaft, into the oximeter sensor,and are exposed through an opening on a bottom surface 730 of the tip.Cable jacket 725 and shaft are wrapped with a tubing 735. Such tubingmay be heat-shrink tubing.

In a specific implementation of FIG. 7, the tip of the retractor has alength of about 17.5 millimeters, width of about 8 millimeters, and athickness (not including the retractor blade) of about 5 millimeters.

FIG. 8 shows a bottom view of the first implementation of a tip 805. Thetip has a retractor blade and slot 810, within which there are sensoropenings. There are four sensor openings for ends of fiber optic cables.The openings 815 a, 815 b, 820 a, and 820 b are for source and detectorfibers.

FIG. 9 shows a perspective view of a second implementation of a tip 905with an encasement 910 which contains optical fiber attached to the tip.

In a specific implementation of FIG. 9, the tip of the retractor has alength of about 17.5 millimeters, width of about 8 millimeters, and athickness (not including the retractor blade) of about 3 millimeters.

FIG. 10 shows a bottom view of the second implementation of a tip 1005.The tip includes a retractor blade and four sensor openings on a bottomsurface 1010 of the tip. The sensor openings include openings 1015 a,1015 b, 1015 c, and 1015 d. Optical fiber is connected to each of thesensor openings. The sensor openings can include sources and detectors.

FIG. 11 shows a perspective view of a third implementation of a tip1105.

FIG. 12 shows a bottom view of the third implementation of a tip 1205.The tip includes two sensor openings on a bottom surface 1210 of thetip. The two sensor openings include an opening 1215 and an opening1220. The openings include a source and detector.

FIG. 13 shows a side view of the third implementation of a tip 1305. Aretractor portion or retractor blade 1310 is at an angle 1315 to a shaft1320 onto which the tip is attached. In an implementation, the angle isabout 90 degrees. Angle 1315 ranges from about 90 degrees to about 179degrees.

In a specific implementation of FIG. 13, the tip of the retractor has alength of about 5 millimeters, width of about 3 millimeters, and athickness (not including the retractor blade) of about 2 millimeters.

FIG. 14 shows a side view of the third implementation of the tip 1405connected to a nerve retractor 1410. This figure shows the handle of theretractor, which connects to the shaft and the tip.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

The invention claimed is:
 1. A device comprising: a retractor, forretracting a tissue, comprising a shaft, a first member coupled to aproximal end of the shaft, and a tip coupled to a distal end of theshaft, wherein the tip comprises a retractor portion and an oximetersensor; a force sensor operatively coupled to the retractor via thefirst member; and a second member, wherein the force sensor comprises afirst connection point and a second connection point, and the firstconnection point of the force sensor is coupled to the first member andthe second member is coupled to the second connection point of the forcesensor.
 2. The device of claim 1 wherein the first connection point andthe second connection point are on opposite sides of each other.
 3. Thedevice of claim 2 wherein the oximeter sensor comprises a first sensoropening and a second sensor opening on a bottom side of the tip.
 4. Thedevice of claim 1 wherein the force sensor comprises a cable which isconfigured to transmit a signal representing an amount of force measuredby the force sensor.
 5. The device of claim 1 wherein the force sensoris a load cell.
 6. The device of claim 1 wherein the force sensor islocated between the first member and the tip of the retractor.
 7. Thedevice of claim 1 wherein the oximeter sensor comprises a first sensoropening and a second sensor opening on a bottom side of the tip.
 8. Thedevice of claim 7 further comprising: a first optical fiber; and asecond optical fiber, wherein the first optical fiber passes through achannel in the shaft and a distal end of the first optical fiber iscoupled to the first sensor opening of the tip, and the second opticalfiber passes through the channel in the shaft and a distal end of thesecond optical fiber is coupled to the second sensor opening of the tip.9. The device of claim 1 wherein the force sensor comprises a cablewhich is configured to transmit a signal representing an amount of forcemeasured by the force sensor, the force sensor is a load cell, the forcesensor is located between the first member and the tip of the retractor,the force sensor has a first end and a second end, wherein the first endand the second end are on opposite sides of each other, and wherein thefirst end of the force sensor is coupled to the first member and thesecond member is coupled to the second end of the force sensor, theoximeter sensor comprises a first sensor opening and a second sensoropening on a bottom side of the tip, and the device comprises: a firstoptical fiber; a second optical fiber, wherein the first optical fiberpasses through a channel in the shaft and a distal end of the firstoptical fiber is coupled to the first sensor opening of the tip, and thesecond optical fiber passes through the channel in the shaft and adistal end of the second optical fiber is coupled to the second sensoropening of the tip.
 10. A device comprising: a retractor, for retractinga tissue, comprising a shaft, a first member coupled to a proximal endof the shaft, and a tip coupled to a distal end of the shaft, whereinthe tip comprises a retractor portion and an oximeter sensor; a forcesensor operatively coupled to the retractor; and a second member,wherein the force sensor has a first end and a second end, the first endand the second end are on opposite sides of each other, and the firstend of the force sensor is coupled to the first member and the secondmember is coupled to the second end of the force sensor.
 11. The deviceof claim 10 wherein the force sensor comprises a cable which isconfigured to transmit a signal representing an amount of force measuredby the force sensor.
 12. The device of claim 10 wherein the force sensoris a load cell.
 13. The device of claim 10 wherein the force sensor islocated between the first member and the tip of the retractor.
 14. Thedevice of claim 10 wherein the oximeter sensor comprises a first sensoropening and a second sensor opening on a bottom side of the tip.
 15. Thedevice of claim 14 further comprising: a first optical fiber; and asecond optical fiber, wherein the first optical fiber passes through achannel in the shaft and a distal end of the first optical fiber iscoupled to the first sensor opening of the tip, and the second opticalfiber passes through the channel in the shaft and a distal end of thesecond optical fiber is coupled to the second sensor opening of the tip.16. The device of claim 10 wherein the force sensor comprises a cablewhich is configured to transmit a signal representing an amount of forcemeasured by the force sensor, the force sensor is a load cell, the forcesensor is located between the first member and the tip of the retractor,the force sensor has a first end and a second end, wherein the first endand the second end are on opposite sides of each other, and wherein thefirst end of the force sensor is coupled to the first member and thesecond member is coupled to the second end of the force sensor, theoximeter sensor comprises a first sensor opening and a second sensoropening on a bottom side of the tip, and the device comprises: a firstoptical fiber; a second optical fiber, wherein the first optical fiberpasses through a channel in the shaft and a distal end of the firstoptical fiber is coupled to the first sensor opening of the tip, and thesecond optical fiber passes through the channel in the shaft and adistal end of the second optical fiber is coupled to the second sensoropening of the tip.
 17. A method comprising: providing a retractor witha first member, a shaft, and a tip having a bottom portion and a bladeportion; forming at least two openings in the bottom portion of theretractor; attaching a force sensor to the first member; and attaching asecond member to the force sensor.
 18. The method of claim 17comprising: connecting a first fiber optic cable to a first opening ofthe at least two openings; and connecting a second fiber optic cable toa second opening of the at least two openings.
 19. The method of claim17 comprising: removing at least a portion of the first member which isnot attached to the force sensor.
 20. The method of claim 17 wherein afirst angle between the second member and the shaft is from about 80degrees to 120 degrees.
 21. The method of claim 20 wherein a secondangle between the blade portion and the bottom portion is from about 90degrees to about 115 degrees.